Multi-Channel GPS Common View Time Transfer Experiments: First Results and Uncertainty Study

摘要

For regular TAI computations, GPS time transfer is currently carried out using a number of common-view observations from single-channel single- frequency C/A code receivers operating in a scheduled mode. This mode of operation limits the accuracy of time transfer and serious problems of ageing of the current receivers are now being encountered. This paper considers all-in- view measurements from multi-channel dual-frequency GPS time receivers used to carry out time transfer between remote locations, taking into account all possible common-view observations for a given baseline. We have used data from Allen Osborne Associates TTR-4P receivers operating at the BIPM, the NPL, the ROA and the USNO. Two approaches have been used. First we construct, for each station, standard 13-minute common-view observations of all available satellites and use these data to compute time differences for three baselines. We find that the results are better than those obtained with single-channel receivers, and are about in accord with what might be expected from the number of measurements. Second we use raw short-term data to compute time differences and compare the results with the standard approach for one baseline. We find that the raw data provide a better measurement of the time link than is possible using the standard approach. In all cases the equipment in use display large variations in the calibration delay that are likely to be induced by the environment and require a corrective action.